High-performance aqueous sodium-ion battery using a hybrid electrolyte with a wide electrochemical stability window.

The practical application of aqueous sodium-ion batteries (ASIBs) is limited by the electrolysis of water, which results in a low working voltage and energy density of ASIBs. Here, a NaClO 4 -based acetonitrile/water hybrid electrolyte (NaClO 4 (H 2 O) 2 AN 2.4 ) is applied to ASIBs for the first time, which effectively extends the electrochemical stability window (ESW) to 3.0 V and reduces the internal resistance of the battery. Based on this hybrid electrolyte, an ASIB full cell using carbon coated Na 2.85 K 0.15 V 2 (PO 4 ) 3 and NaTi 2 (PO 4 ) 3 as the cathode and anode materials, respectively, can afford a discharge capacity and energy density of 52 mA h g -1 and 51 W h kg -1 , respectively, at a current density of 1 A g -1 . The energy density of this battery exceeds almost all reported traditional ASIBs.